In the OTN (Optical Transport Network) standardized by the ITU-T Recommendation, a client signal is mapped to ODUk (Optical channel Data Unit) (where k=0, 1, 2, 3, 4, etc., for example). A lower order ODUk (LO ODUk) is multiplexed into a higher order ODUk (HO ODUk) by the time division multiplexing so as to be transmitted. 100 Gbps data is transmitted in ODU4, for example. Schemes for transmitting large-volume data of more than 100 Gbps over the OTN have recently been considered.
Techniques to realize transmission of large-volume data are described in Japanese Laid-Open Patent Publication No. 2012-119759, Japanese Laid-Open Patent Publication No. 2010-062682, and Japanese Laid-Open Patent Publication No. 2009-159062, for example.
Transmission of a high-speed signal of more than 100 Gpbs over the OTN may be realized by defining a frame of a higher order than the ODU4, for example. A frame realizing a bit rate n times higher than a bit rate of the ODU4 is referred to as “ODU4Cn (or ODUCn)”. For example, ODU4C2 has a transmission capacity approximately twice as large as that of the ODU4, and ODU4C4 has a transmission capacity approximately four times larger than that of the ODU4.
It is, however, difficult to realize a symbol rate of 100 Gbaud or more because of a limit of increase in high speed of hardware circuits.